Effect of Rituximab on Immunological Recall Response to Specific Antigens in the Treatment of Non-Hodgkin's Lymphoma

Inclusion Criteria: * Signed IRB-approved informed consent. * Age \>/=40 years. * Men and women of reproductive potential who are following accepted birth control methods. * Histologic confirmation of low-grade or follicular, B-cell NHL prior to study entry. * Relapsed (maximum of 5 relapses) or refractory, low-grade or follicular, CD20+,B-cell NHL. * WHO performance status \</= 2. * Expected survival \>/= 1 year. * Acceptable hematologic status, liver function, renal function, and pulmonary function. * Patients must be recovered from all nonhematological toxicities associated with prior surgery, radiation treatments, chemotherapy, biological therapy, bone marrow transplant, investigational drugs, or immunotherapy. * Known history of tetanus toxoid immunization or positive tetanus titer at the screening visit. Exclusion Criteria: * Active autoimmune disease. * Exposure to rituximab within 12 months prior to Day 1. * Chemotherapy within 3 months prior to Day 1. * Previous immunization with tetanus toxoid within 2 years prior to Day 1. * Previous exposure to KLH. * Receipt of intravenous or intramuscular immunoglobulin (IVIG or IMIG) within 30 days of Day 1. * Known history of hepatitis or other hepatic disease, HIV infection, or AIDS. * Current use (including "recreational use") of any illicit drugs or history of drug or alcohol abuse within the 5 years prior to Day 1. * Prior diagnosis of aggressive NHL or mantle-cell lymphoma. * Chronic lymphocytic leukemia (CLL). * Small lymphocytic lymphoma (IWF A) with peripheral blood lymphocyte count \> 5,000 cells/mm3. * History of other primary malignancy, with the exception of squamous cell carcinoma or basal cell carcinoma of the skin, in situ carcinoma of the cervix, or treated prostate cancer for which the subject has not been disease free for at least 3 years. * Serious nonmalignant disease (e.g., congestive heart failure, hydronephrosis); active, uncontrolled bacterial, viral, or fungal infection; or any other condition that would compromise protocol objectives in the opinion of the investigator and/or sponsor. * Known allergies or contraindications to tetanus toxoid or KLH. * Known allergy to shellfish. * Presence of protein-losing enteropathy. * Major surgery, other than diagnostic surgery, within 4 weeks prior to Day 1. * Participation in another clinical study with an investigational agent or device within the last year. The subject cannot participate in any other clinical study with an investigational agent or device during the course of this study. * Pregnant or lactating female subjects